1. Field of the Invention
The present invention relates to a linear motion guide unit envisaged to treat well high speed and high cycle in modern advanced machines such as semiconductor manufacturing equipments, industrial robots, engines, and so on, and more particularly a linear motion guide unit in which sintered resinous material of porous structure is installed in a carriage to provide a return passage therein while a joint tube communicates the return passage with turnarounds formed in the end caps.
2. Description of the Prior Art
The conventional linear motion guide units are commonly so constructed that a slider is movable relatively of an elongated track rail through many rolling elements, which are allowed to run through recirculating circuits comprised of load areas of raceways defined between the track rail and the slider, and non-loaded areas including turnarounds in end caps and return passages in a carriage in the slider. To help prevent metal-to-metal direct contact between the rolling elements and the recirculating circuits thereby to make certain of the rated durability of the linear motion guide units, it is necessary to continue constantly supplying the rolling elements and the recirculating circuits with lubricant to ensure keep lubrication between the rolling elements and the recirculating circuits. Secure lubrication between the recirculating circuits and the rolling elements is usually realized by periodic replenishment of lubricant.
Recently remarkable needs in reduction of expenditure on maintenance activities as well as in energy savings have given birth to various advanced machines such as semiconductor manufacturing equipments, industrial robots, engines, and so on, which can operate on maintenance-free. Correspondingly, the linear motion guide units to be used in the machinery are also counted on meeting with needs of maintenance-free lubrication. Especially, the linear motion guide units expected incorporated in the semiconductor manufacturing equipment, and so on, which conform the clean-room specifications must meet demands to adopt specific substances and/or designs that might yield little or no debris or cutting. Moreover, it is inevitable to limit the amount of lubricant used as least as possible since fine mist of lubricant might contaminates the atmosphere in the clean room.
A prior linear motion guide unit is disclosed in Japanese Patent Laid-Open No. 161354/2000, in which a ball-recirculating circuit is composed of a linear area bored in a carriage of a slider, and a curved area formed in an end cap, and the linear area is connected with the curved area through a socket-and-spigot joint that is made up of a hollow spigot end to extend an open end of the curved area into the linear area of the carriage, and a receptacle formed in an open end of the linear area to receive and fit over the spigot end. With the prior linear motion guide unit constructed as stated above, the end cap is made with a roughly cylindrical spigot while the carriage is made with a roughly socket to receive therein the spigot to communicate the linear area in the carriage with the curved linear area in the end cap to complete the ball-circulating circuit. In the prior linear motion guide unit, however, the linear area in the ball-recirculating circuit has no sintered resinous material as will be recited later, and moreover a guide member to define a radially inside curved area, because made apart from the end cap, has to be assembled into the end cap in conformity with the curved area in the end cap. It will be said this construction is unfit for the machines that need maintenance-free operation.
Another conventional linear motion guide unit is disclosed in Japanese Patent Laid-Open No. 136805/1986, in which a circulating circuit provided by combination of a slider with a guide rail is made up of a load raceway defined between a raceway groove on the guide rail and a raceway groove in a carriage of the slider, a return passage bored in the carriage in parallel with the load raceway, and curved ways formed in end caps of the slider one to each end cap. The return passage is made with a tube fit forcible into a hole drilled through the carriage. However, since the tube for the return passage is forcibly fit in the through-hole in the carriage, replacement with new one is very tough job.
Although but the prior linear motion guide units recited just above can operate successfully with no application of lubricant so long as used under light loads in the clean room specifications, they do not always serve well for the recently advanced machinery that has become increasingly higher in speed and oscillation. With the prior lubricant-containing polymer member availed for the conventional linear motion guide units, the polymer should be molded while being mixed with lubricating oil. In addition, the lubricant-containing polymer member, because of lacking the necessary strength in itself and of itself, has to be reinforced when incorporated really in the linear motion guide units. To cope with these disadvantages, the linear motion guide unit has inevitably become sophisticated in construction and highly advanced technology has been needed. With the construction in which the lubricating plates were mounted on the slider to make sliding engagement with the track rail, there is the problem that the slider has caused large frictional resistance when it was applied to machinery high in speed and oscillation.
Modern advanced machinery has a tendency to get higher in working speed and oscillation. These days, to deal with the tendency, the linear motion guide unit in which a return passage is made with a sintered resinous material of porous structure has been used in practice. An example of the linear motion guide unit having the return passage of sintered resinous material of porous structure stated just above is disclosed in, for example Japanese Patent Laid-Open No. 82469/2001, which is a senior application of the same applicant. With the linear motion guide unit recited earlier, the return passage bored in the slider is lined with sintered resinous material of porous structure, which can make certain of supplying the rolling elements with lubricant for a prolonged period, refining the slider in durability. The slider movable relatively to the track rail by virtue of the rolling elements is made therein with a through-hole in which a sleeve of the sintered resinous material having porous structure fits to form a return passage encircled with the sintered resinous material. Grease, lubricating oil and so on is absorbed in the porous structure of the sintered resinous material in a way continuing to be supplied for a long period onto the rolling elements running through the return passage, thereby lubricating the raceway via the rolling elements to improve the slider in durability as well as reduce the sliding resistance that is encountered when the slider moves on the track rail.
Thus, it may be worthwhile developing a linear motion guide unit continuing to supply the rolling elements with lubricant, thereby making certain of smooth running of the rolling elements for a prolonged period. To this end, it remains a major challenge to provide a linear motion guide unit in which the rolling elements running through the return passage in the slider are allowed to roll smoothly at a joining area of the return passage together with the associated turnaround, and the material fit in the through-hole in carriage of the slider to define the return passage has a property of self-lubrication of lubricating oil onto the rolling elements and also a strength enough of itself to need not to be reinforced with any other means.
The present invention has for its primary object to overcome the challenge as described just above, especially provide a linear motion guide unit in which a sleeve of sintered resinous material capable of impregnated with lubricant fits in a through-hole bored in a carriage to form a return passage, and a joint tube is applied at a junction of a turnaround in an end cap with any one of forward and aft ends of the sleeve to make sure of smooth rolling of the rolling elements at the junction. The present invention provides a linear motion guide unit made free from maintenance such as periodic application of lubricant and/or suppliance of lubricating oil to the rolling elements running through the recirculating circuit made up of a load raceway, turnarounds and a return passage, even under the severe operating conditions in atmosphere and/or subjected load. The present invention also provides a linear motion guide unit in which the joint tube applied at a junction of the turnaround with the return passage contributes to reducing the sliding resistance that might be encountered when the rolling elements run through the recirculating circuit used in the high-speed, high-cycle machines, thereby realizing inexpensive lubrication.
The present invention is concerned with a linear motion guide unit comprising, a track rail provided on sidewise opposing sides thereof with first lengthwise raceway grooves, one to each side, a slider having second raceway grooves confronting the first raceway grooves and fitting over the track rail in a way movable lengthwise with respect to the track rail, and more than one rolling element allowed to run through load raceways defined between the first raceway grooves on the track rail and the second raceway grooves in the slider, wherein the slider is comprised of a carriage having the second raceway grooves thereon and through-holes extending therein along the second raceway grooves, sleeves fit in the through-holes, one to each through-hole, in a way lining the through-hole with only forward and aft ends of the through-hole being left naked, thereby providing a major area of a return passage, spacers arranged on forward and aft ends of the carriage, one to each end, the spacers each having a radially inside curved half for a turnaround to connect the load raceway and the return passage and also having an inside part for a joint tube to make up for any one end of the return passage joining with the radially inside curved half after fitted in the naked end of the through-hole, and end caps arranged on outside ends of the spacers, one to each outside end, the end caps each having a radially outside for the turnaround and also having an outside part for the joint tube to make up for any one end of the return passage joining with the radially outside curved half after fitted in the naked end of the through-hole.
In an aspect of the present invention, there is disclosed a linear motion guide unit in which the sleeve fit in the through-hole in the carriage is made of sintered resinous material of porous structure capable of carrying lubricant therein. In another aspect of the present invention there is disclosed a linear motion guide unit in which the sleeve is made in such a contour of circle in cross section as to conform to the through-hole in the carriage and also has a linear hole therein provide the return passage.
In another aspect of the present invention, moreover, there is disclosed a linear motion guide unit in which the inside part of the spacer and the outside part of the end cap are matched up together to form the joint tube that makes end-to-end abutment against the sleeve to make up for the end of the return passage to complete the return passage lying in alignment with the linear hole in the sleeve to connect between the return passage and the turnaround.
In a further another aspect of the present invention there is disclosed a linear motion guide unit in which the inside part is made to account for a minor part less than half the circle in cross section of the joint tube, while the outside part is a major part larger than half the circle of the joint tube, so that the inside and outside parts are joined together to form the joint tube at their mating edges lying lopsided with respect to the plane lying on the axis of the joint tube. In another aspect of the present invention there is disclosed a linear motion guide unit in which the joint tube made up of the inside and outside parts is made in a straight tube.
In a further another aspect of the present invention there is disclosed a linear motion guide unit in which the radially inside curved half for the turnaround on the spacer corresponds to the load raceway, while the inside part for the joint tube corresponds to return passage. In another aspect of the present invention there is disclosed a linear motion guide unit in which the spacer is comprised of a transverse body interposed between the end cap and the spacer, and lugs integral with the body and each having the radially inside curved half for the turnaround and the inside part for the joint tube. In another aspect of the present invention there is disclosed a linear motion guide unit in which end seals are mounted on end faces of the end caps, one to each end face.
With the linear motion guide unit of the present invention, especially, the carriage is made of metal whereas the sleeve for return passage discussed here is made of sintered resinous material relatively fragile compared with metal. Nevertheless, the sleeve is held in the through-hole with zero fit in which there is no clearance between the sleeve and the through-hole in the metal carriage and/or with clearance fit, that is, with any clearance fit having any positive or zero allowance, instead of force fit in which interference always results on assembly of the sleeve in the through-hole. Thus, there is no occurrence of breakage such as cracks in the sleeve for return passage. Moreover, the clearance fit on assembly of the sleeve in the carriage contributes to no possibility of the occurrence of any breakage in the sleeve, which might result from the difference in thermal expansion between the carriage and the sleeve, thus making ensure high durability of the sleeve for return passage.
With the linear motion guide unit constructed as stated earlier, the joint tube made up of the outside part on the end cap and the outside part on the spacer is effective to make certain of extremely steady junction of the return passage with the turnaround, and connect between the return passage and the turnaround with precision and smoothness to thereby reduce the sliding resistance that is encountered when the rolling elements run over the junction, helping the rolling elements roll smoothly. That is to say, according to the linear motion guide unit of the present invention, the joint tubes are arranged to make end-to-end abutment against the forward and aft edge of the sleeve to complete the return passage, and in doing so establish the smooth passage in the whole time of recirculation, thus making sure the rolling elements smoothly run through the overall recirculating circuit.
The sleeve for return passage is made of sintered resinous material of porous structure taking on the function of an absorber readily soaking up lubricating oil or grease. Thus, the sleeve soaked with the lubricating oil or grease can perform proper lubrication of the rolling elements. That is to say, the lubricating oil or grease absorbed and reserved in the porous structure is transferred little by little to the rolling elements when making contact with the rolling elements. The lubricant adhered on the rolling elements is then applied to the load raceways as the rolling elements run through the load raceways. The sleeve for return passage made of sintered resinous material has sufficient strength in itself and on itself even with no other reinforcement. Moreover, the sintered resinous material used in the present invention, as being less subjected to wear, is tough to clogging in the porous structure, which might be caused by cuttings, debris, and so on occurring due to wear, thereby to make it possible to continue supplying over a prolonged period the rolling elements with lubricant, which is reserved in the porous structure.
Moreover, the sleeve made of sintered resinous material is flanked by the joint tubes at the forward and aft ends thereof. This construction can keep the sintered resinous material of the sleeve away from the threat that the balls might batter away on the sleeve at the entrance to the return passage, helping the sleeve of sintered resinous material survive for a long period.
Consequently the linear motion guide unit of the present invention is made free from maintenance such as periodic application and/or suppliance of lubricant over the prolonged period. Until the lubricant is consumed transferred from the return passage to the rolling elements, there is no need to replenish the return passage with lubricant. Moreover, the linear motion guide unit of the present invention lessens the sliding resistance at the load raceway to the extent conforming to the high speed and high cycle of the machines.
Other aspect and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed preferred embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.